1. Field of the Invention
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device which has favorable daylight contrast and white luminance and excellent color reproducibility and includes an absorption material.
2. Description of the Related Art
A flat panel display such as a liquid crystal display device (hereinafter, also referred to as LCD) has been used in a broadening range of fields every year as an image display device which has low power consumption and saves spaces. A liquid crystal display device has a constitution in which a backlight (hereinafter, also referred to as BL), a backlight-side polarizing plate, a liquid crystal cell, a viewer-side polarizing plate, and the like are provided in this order.
In the recent flat panel display market, for liquid crystal display devices, development for power saving, high definition, and color reproducibility improvement has been underway in order to improve LCD performance. At the moment, while there is a significant demand for power saving, high definition, and color reproducibility improvement particularly in small-sized display devices such as tablet PCs and smartphones, development of next-generation Hi-visions (4K2K, EBU ratio of 100% or higher) with current TV standards (FHD, 72% of National Television System Committee (NTSC) ratio≈100% of European Broadcasting Union (EBU) ratio) is also underway for large-sized display devices. Therefore, there is an intensifying demand for power saving, high definition, and color reproducibility improvement in liquid crystal display devices.
From the viewpoint of improving color reproducibility, a method for sharpening the light emission spectrum of a backlight has been known. For example, JP2012-169271A describes a method for increasing luminance and improving color reproducibility by realizing white light using a quantum dot (QD) which emits red light and green light as a fluorescent body between a blue LED and a light guide plate. In SID'12 DIGEST p. 895, a method of combining a light conversion sheet (QDEF, also referred to as quantum dot sheet) in which a quantum dot is used in order to improve the color reproducibility of the LCD is proposed.
Meanwhile, an increase in the size of displays or distribution of tablet PCs broadens the operation environment of displays, and improvement of visibility in bright places such as immediately under sunlight or bright indoor lighting has been becoming more important.
Generally, an antireflection function is provided to the display screen of an LCD in order to enable an observer to easily view images. This function can be realized using an anti-reflection film or an anti-glare film. Examples of an ordinary anti-reflection film include an anti-reflection (AR) film or a low reflection (LR) film which is obtained by forming a film having a different refractive index from that of a substrate on the surface of the substrate so as to reduce reflection using an interference effect between light reflected on the surface of the substrate and light reflected on the surface of the formed film. In addition, additional examples of an ordinary anti-glare film include an anti-glare (AG) film which is obtained by forming a film having a fine uneven pattern on the surface of a substrate and includes an anti-glare layer that prevents the mirror-like reflection of images using the scattering effect of light.
However, some of light entering a liquid crystal display device is transmitted through the anti-reflection film or the anti-glare film on the surface and the rest of the light is reflected on the surface of an electrode or the like or the glass surface of a cell in a liquid crystal cell. This is referred to as internal reflection.
Particularly in a case in which a display has a high definition, it is known that glare deteriorates due to interference between pixels of an LCD and the unevenness of an anti-glare layer on the panel surface, and thus suppression of internal reflection becomes more important.
As a method for suppressing internal reflection, a method in which a λ/4 phase difference plate or a λ/2 phase difference plate is disposed between a polarizer of a viewer-side polarizing plate and a liquid crystal cell is proposed (refer to WO2012/043375A).
In addition, in JP2008-203436A, use of an optical filter having a maximal absorption in each of a wavelength range of 380 nm to 420 nm, a wavelength range of 480 nm to 520 nm, and a wavelength range of 585 nm to 620 nm in an image display device, particularly, a self-light emission image display device such as a plasma display is proposed in order to suppress degradation of contrast in bright places and improve color reproducibility.
In JP2011-7995A, a method in which, in a projector and a projection screen, a projector light source having a peak at a wavelength different from a plurality of peak wavelengths in a light source spectrum of external light is used, and a color material having an absorption band including a wavelength overlapping with at least one of a plurality of the peak wavelengths of external light is provided in the projection screen is proposed. JP2011-7995A describes that, according to the above-described constitution, it is possible to efficiently absorb external light (that is, unnecessary light) having a light emission peak different from that of the projected light from the projector using the color material, and the light intensity of the external light can be selectively reduced, and thus images with high contrast can be displayed.